A human ecology theoretical framework for the study of sexual differentiation in metropolitan area professional occupations is presented in this paper. Human ecology theory attempts to describe characteristics of organizations for a population as a whole. Differences in the characteristics of organizations among populations represent the fundamental human ecological problem. This theory describes sexual differentiation within occupations as a function of occupational organizations. The focus of sexual differentiation is occupational structure, since across populations individuals are differentially allocated to occupations (and industries), often on the basis of age, race, and sex. By using a human ecology research model, it is hoped that differences in organizations within metropolitan areas will explain, at least in part, variations in sexual differentiation. (MK)